This recipe was born from a desire to *something more interesting* with whole wheat bread beyond adding other flours or seeds to it. It was also around Thanksgiving, so sweet potatoes were everywhere. The color is beautiful; it has a nice moistness. It makes great toast, and wonderful grilled sandwiches all the year 'round. And stuffing - oh, yeah. Strata - oh my.
Whole grain breads, especially weighty ones like this can be a challenge. Please read Step 3, about the rest period, carefully. —boulangere
If using leftover sweet potatoes, including whatever you have stirred into them (except of course marshmallows) because it will only make the bread more interesting, warm them up a bit before adding to the dough. If using freshly cooked and mashed, let them cool to where they are comfortable to the touch.
Measure water into bowl of a stand mixer fitted with the dough hook. Sprinkle yeast over and whisk to blend. Add the flours, salt, canola oil, and sweet potatoes. Mix on low speed until dough comes together and flours are hydrated.
Turn mixer off and drape a piece of plastic around the top of the bowl. Let the dough rest (autolyse) for 20 minutes. This allows the large particles of whole wheat flour to fully inflate themselves with water. Without that time, your dough will tend to look dry and broken. You'll be tempted to add water, and just at the point where it's all absorbed, suddenly it turns into too much, and the dough goes all limp and sticks to the bowl. So then you'll decide to add more flour, and by that time, you will have firmly lodged yourself right behind the 8 ball. So go for the rest period and leave the 8 ball where it belongs.
After the rest period, remove the sheet of plastic and turn mixer on to lowest speed. I never get tired of seeing the miracle of a dough gather its skirts under itself, and come together in a beautiful waltz around the dough hook. That, my friends, is all because of the rest period. Continue kneading for a couple of minutes. Stop mixer. Pull off a walnut-size piece of dough. Round it up quickly between your palms. Then gently tease it out over your fingertips. You are trying to achieve a *windowpane*. In other words, you want to see how thin you can get the dough without it tearing. This tells you if you have adequately developed the gluten - something that won't happen well in whole grain breads without the rest period. If your dough tears, return your piece to the bowl and knead for a couple of minutes more. Repeat windowpane. You should be there by now.
Turn dough out of bowl. Oil bowl and return dough, turning it over from top to bottom. Cover with your piece of plastic and allow to proof until you can gently press the surface with a finger, and the indentation remains.
Gently turn dough out onto a lightly floured surface and divide in half. Either shape and drop into 2 conventional loaf pans, or shape into hearth loaves that you'll set onto baking sheets lined with parchment. Dust the surface of each loaf with flour and gently drape with plastic. Again allow to proof until the surface holds the indentation of your finger.
Meanwhile, preheat oven to 375 degrees. Just before placing loaves in oven, slash each 3 or 4 times a good 1/4" deep with a serrated knife held at an acute angle. Bake them for 40 minutes, rotating and the 20-minute point. Bread is done when you get a temperature reading of 185 degrees at the dead center.
Remove from oven and cool on racks. Begin planning all the wonderful sandwiches you're going to make with it.